/**
 * @file calmas.cpp
 * @brief Nodal mass/inertia assembly routine
 * 
 * This routine assembles nodal masses and inertias from various element types (solids, shells, beams)
 * and handles mass scaling and parallel communication in MPP (Massively Parallel Processing) environments.
 * 
 * Key functionality:
 * - Initializes mass/inertia matrices
 * - Adds nodal masses from structural elements
 * - Transfers mass from different element types (solids, shells, beams) to nodes
 * - Handles SPH (Smoothed Particle Hydrodynamics) nodes specially
 * - Applies mass scaling if requested
 * - Manages mass transfer between master/slave nodes
 * - Handles parallel communication for distributed memory systems
 * 
 */

#include <vector>
#include <algorithm>

// Constants and type definitions
using Real = float; // Using _Real_ as requested, though double might be more typical for precision

// Structure to hold node information (simplified representation)
struct NodeData {
    std::vector<Real> mass;          // Nodal mass values (size = 6*NUMNP)
    std::vector<std::vector<Real>> inertia; // 3x3 inertia matrices (size = 3x3xNUMNP)
};

// Structure for element connectivity
struct ElementConnectivity {
    std::vector<int> node_indices;    // Node indices for the element
    int type;                        // Element type identifier
};

// Main function for nodal mass assembly
void calculateNodalMass(
    NodeData& node_data,                   // Output: Nodal mass and inertia data
    const std::vector<Real>& element_mass, // Input: Element masses
    const std::vector<ElementConnectivity>& elements, // Input: Element connectivity
    const std::vector<int>& node_types,    // Input: Node type identifiers
    const std::vector<Real>& added_mass,   // Input: Additional nodal masses
    bool use_mass_scaling = false,         // Input: Flag for mass scaling
    Real mass_scaling_factor = 1.0,        // Input: Mass scaling factor
    Real time_step_scale = 0.0,            // Input: Time step scaling factor
    bool is_parallel = false               // Input: Flag for parallel execution
) {
    const int num_nodes = node_data.mass.size() / 6;
    const int num_elements = elements.size();
    
    // Initialize node flags and mass/inertia
    std::vector<int> node_flags(num_nodes, 0);
    
    // Flag special nodes (rotational, SPH, etc.)
    for (int i = 0; i < num_nodes; i++) {
        if (node_types[i] == 2) { // Rotational nodes
            node_flags[i] = 2;
        } else if (node_types[i] == 1) { // SPH nodes
            node_flags[i] = 1;
        }
    }
    
    // Initialize mass and inertia matrices
    for (int i = 0; i < num_nodes; i++) {
        // Only initialize for non-SPH and non-rotational nodes
        if (node_flags[i] != 1 && node_flags[i] != 2) {
            node_data.inertia[i][0][0] = 1.0;
            node_data.inertia[i][0][1] = 0.0;
            node_data.inertia[i][0][2] = 0.0;
            node_data.inertia[i][1][0] = 0.0;
            node_data.inertia[i][1][1] = 1.0;
            node_data.inertia[i][1][2] = 0.0;
            node_data.inertia[i][2][0] = 0.0;
            node_data.inertia[i][2][1] = 0.0;
            node_data.inertia[i][2][2] = 1.0;
        }
        
        // Initialize mass for non-SPH nodes
        if (node_flags[i] != 1) {
            for (int j = 0; j < 6; j++) {
                node_data.mass[6*i + j] = 0.0;
            }
        }
    }
    
    // Add nodal masses from input
    for (int n = 0; n < added_mass.size()/6; n++) {
        int node_idx = /* get node index from added_mass data */;
        if (node_flags[node_idx] != 1) { // Skip SPH nodes
            for (int j = 0; j < 3; j++) {
                node_data.mass[6*node_idx + j] = added_mass[6*n + j];
            }
            
            // Average rotational inertia components
            Real rot_inertia = (added_mass[6*n + 3] + added_mass[6*n + 4] + added_mass[6*n + 5]) / 3.0;
            for (int j = 3; j < 6; j++) {
                node_data.mass[6*node_idx + j] = rot_inertia;
            }
        }
    }
    
    // Transfer mass from solid elements to nodes
    const Real face_factor = 10.0/36.0; // Mass distribution factor for face nodes
    const Real acc_factor = 40.0/27.0;  // Mass distribution factor for edge nodes
    
    for (int elem_idx = 0; elem_idx < num_elements; elem_idx++) {
        const auto& elem = elements[elem_idx];
        Real elem_mass = element_mass[elem_idx] / /* density term */;
        
        // Handle different element types
        switch (elem.type) {
            case 0: // Brick elements
            case 1: // Other brick type
                for (int node_pos = 0; node_pos < elem.node_indices.size(); node_pos++) {
                    int node_idx = elem.node_indices[node_pos];
                    for (int j = 0; j < 3; j++) {
                        node_data.mass[6*node_idx + j] += elem_mass;
                    }
                }
                break;
                
            case 2: // 10-node tetrahedrons
                // Corner nodes
                for (int node_pos = 0; node_pos < 4; node_pos++) {
                    int node_idx = elem.node_indices[node_pos];
                    for (int j = 0; j < 3; j++) {
                        node_data.mass[6*node_idx + j] += elem_mass * face_factor;
                    }
                }
                // Edge nodes
                for (int node_pos = 4; node_pos < 10; node_pos++) {
                    int node_idx = elem.node_indices[node_pos];
                    for (int j = 0; j < 3; j++) {
                        node_data.mass[6*node_idx + j] += elem_mass * acc_factor;
                    }
                }
                break;
                
            case 3: // 4-node tetrahedrons
                for (int node_pos = 0; node_pos < 4; node_pos++) {
                    int node_idx = elem.node_indices[node_pos];
                    for (int j = 0; j < 3; j++) {
                        node_data.mass[6*node_idx + j] += elem_mass;
                    }
                }
                // Additional node for this type
                int extra_node_idx = /* get extra node index */;
                for (int j = 0; j < 3; j++) {
                    node_data.mass[6*extra_node_idx + j] += elem_mass;
                }
                break;
        }
    }
    
    // Apply mass scaling if requested
    if (use_mass_scaling || time_step_scale > 0.0) {
        // Calculate scaling factors for each node (simplified)
        std::vector<Real> mass_scaling(num_nodes, 1.0);
        std::vector<Real> rot_scaling(num_nodes, 1.0);
        
        // Apply scaling to nodal masses
        for (int node_idx = 0; node_idx < num_nodes; node_idx++) {
            if (node_flags[node_idx] != 1) { // Skip SPH nodes
                // Translation mass scaling
                for (int j = 0; j < 3; j++) {
                    node_data.mass[6*node_idx + j] *= mass_scaling[node_idx] * mass_scaling[node_idx];
                }
                // Rotational mass scaling
                for (int j = 3; j < 6; j++) {
                    node_data.mass[6*node_idx + j] *= rot_scaling[node_idx] * rot_scaling[node_idx];
                }
            }
        }
    }
    
    // Handle parallel communication if needed
    if (is_parallel) {
        // Simplified parallel communication - would need MPI in real implementation
        // commSendReceive(node_data.mass, ...);
        // commSendReceive(node_data.inertia, ...);
    }
}